As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues have resulted in the development of three-dimensional designs, such as a fin field effect transistor (FinFET). A typical FinFET is fabricated with a thin vertical “fin” (or fin structure) extending from a substrate formed by, for example, etching away a portion of a silicon layer of the substrate. The channel of the FinFET is formed in this vertical fin. A gate is provided over (e.g., wrapping) the fin. Having a gate on both sides of the channel allows gate control of the channel from both sides. In addition, strained materials in source/drain (S/D) portions of the FinFET utilizing selectively grown silicon germanium (SiGe) may be used to enhance carrier mobility.
However, there are challenges to implementation of such features and processes in complementary metal-oxide-semiconductor (CMOS) fabrication. For example, non-uniform composition distribution of a fin structure causes fluctuation of FinFET characteristics such as increased leakage current, thereby degrading the device performance. As the gate length and spacing between devices decrease, these problems are exacerbated.